1. Field of the Invention
The present invention relates to a process for producing acrylic synthetic fibers having anti-pilling properties, and more specifically to a process for producing acrylic synthetic fibers highly resistant to pilling, and with respect to dyeability, not inferior to conventional ones, in which process the condition of the primary stretching (the general term of the cold stretching immediately after spinning and the hot stretching given subsequently to the water-washing after the cold stretching), the internal water content of the water-swollen gel fibers, the conditions of the steps of drying-compacting, secondary stretching and relaxing heat treatment are specified.
2. Description of the Prior Art
It is well known that acrylic synthetic fibers have a wide field of applications in textile materials and room furnishing materials because of their wool-like soft hand and excellent dyeability.
However, it is not that such acrylic synthetic fibers excellent in usefulness have no defect in practical use, and in effect in certain fields of their applications it has been strongly demanded to establish quickly industrial means for improving fiber properties.
Although the resistance to abrasion and resistance to fibrillation of acrylic synthetic fibers can almost satisfy the practical level demanded for textile materials, etc., woven or knitted fabrics produced from acrylic synthetic fibers have a defect that small balls of entangled short fibers, the so-called "pills," are generated on the surface of the fabrics with the passage of wearing time and greatly lower the commercial value.
The generation of such pills is not a problem peculiar to acrylic synthetic fibers, but is a trouble in practical use widely observed also in polyamide fibers or polyester fibers. The generation of pills in woven or knitted fabrics obtained from acrylic synthetic fibers can be said rather less in comparison with the case of polyamide fibers or polyester fibers, but even then considerable formation of pills is observed as compared with woven or knitted fabrics obtained from wool fibers. This has been a cause that acrylic synthetic fibers cannot be satisfactorily substituted for wool fibers as a fabric-forming material.
Therefore, to prevent such generation of pills, several industrial means have been heretofore employed. It is described, for example, in Japanese Patent Publication No. 5863/1973, that the resistance to pilling of acrylic synthetic fibers can be grasped as a correlation of single-filament denier and strength characteristics, and in Japanese Patent Publication No. 18195/1964, that in order to impart resistance to pilling to woven fabrics made from acrylic synthetic fibers, the fabrics are treated with an aqueous solution of aniline, aniline acetate, aniline hydrochloride, or aniline sulfate.
However, in practice, the former uses acrylic synthetic fibers of considerably large single-filament deniers and therefore if the fibers are used as a material for forming carpets, a certain degree of usefulness can be acknowledged but no substantial applicability was observed for purposes as general textile-forming material. The latter process poses a fundamental question as to its usefulness in respect to odor and coloring.
Recently, Japanese Patent Application Laid-Open Nos. 80323/1974 and 35121/1973 propose processes for producing anti-pilling acrylic synthetic fibers which are lowered in fiber properties, especially in elongation. These processes also involve unsolved problems. For example, because of too high a content of acrylonitrile, which is the acrylic fiber-forming component, it is impossible to obtain dyed products which can ensure a satisfactory level of deep color. Therefore, the practice on an industrial scale remains as a problem.
Thus, although technical means have been attempted to obtain anti-pilling fibers by modifying the production condition of acrylic synthetic fibers, it has been extremely difficult to obtain a favorable balance of single-filament strength, elongation and fiber dyeability at the same time.